Leakage protection method for multi-parameter sampling of mine power supply system

Abstract

The invention provides a leakage protection method for multi-parameter sampling of a mine power supply system, which comprises the following steps of: respectively connecting three sampling capacitors into A, B and C phases of the power supply system, connecting the other ends of the three sampling capacitors through a miniature current transformer to form an artificial neutral point, and grounding the artificial neutral point through a primary side of another miniature current transformer; monitoring the power supply system and calculating a power supply system personal electric shock current equivalent steady-state effective value, a power supply system personal electric shock current transient effective value, a power supply system zero-sequence voltage effective value, a power supply system zero-sequence voltage change rate, a power supply system zero-sequence voltage instantaneous value and a power supply system phase-to-ground voltage effective value; acquiring the waveform shape of the sampling current according to the change rate of each phase of ground voltage of the power supply system and the instantaneous value of each phase of ground voltage of the power supply system; and judging a fault according to the calculation data, and enabling a protection device to act to complete leakage protection. The equipment manufactured by the invention is small in size and convenient to install and maintain, and the failure rate of the equipment can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of leakage protection of mine power supply systems, and in particular relates to a leakage protection method for multi-parameter sampling of mine power supply systems. Background Art

[0002] In the leakage protection device of the coal mine power supply system, sampling of zero-sequence voltage is essential. The traditional zero-sequence voltage sampling method is measured by a three-phase five-column voltage transformer. An iron core column is added on both sides of the three-column iron core as a closed magnetic circuit of the zero-sequence magnetic flux, and a set of secondary windings can be added to form an open triangle to obtain 3 times the zero-sequence voltage. However, in the system where the neutral point of the coal mine transformer is not grounded, the primary neutral point of the three-phase five-column voltage transformer must be grounded, which actually changes the grounding method of the system, which may bring potential safety hazards, such as the possibility of forming a series resonance overvoltage. In addition, due to the large size of the three-phase five-column voltage transformer, it is necessary to comprehensively consider factors such as installation location, wiring and protection during installation, which further increases the difficulty and cost of installation. The proposed capacitor coal mine power supply system zero-sequence voltage sampling method will not actually change the neutral point grounding method of the system, reduce the difficulty and cost of installation, and can simultaneously measure the steady-state component and transient component of the zero-sequence voltage. Summary of the invention

[0003] The purpose of the present invention is to provide a leakage protection method for multi-parameter sampling of a mine power supply system, which can realize sampling of multiple parameters without changing the neutral point grounding mode of the power system. The insulation monitoring of the power supply system to the ground and single-phase leakage protection are realized through multiple parameters.

[0004] The technical solution of the present invention is as follows:

[0005] The present invention provides a leakage protection method for a mine power supply system, comprising:

[0006] Step 1: Connect three sampling capacitors to the A, B, and C phases of the power grid respectively, and connect the other ends together through a micro current transformer to form an artificial neutral point, which is then grounded through the primary side of a micro current transformer.

[0007] Step 2, monitor the above-mentioned power supply system and calculate the equivalent steady-state effective value of the electric shock current of the power supply system, the transient effective value of the electric shock current of the power supply system, the effective value of the zero-sequence voltage of the power supply system, the rate of change of the zero-sequence voltage of the power supply system, the instantaneous value of the zero-sequence voltage of the power supply system, the effective value of each relative ground voltage of the power supply system, the rate of change of each relative ground voltage of the power supply system and the instantaneous value of each relative ground voltage of the power supply system, and collect the waveform shape of the sampled current;

[0008] Step 3: determine the fault based on the above calculation data, activate the protection device, and complete the leakage protection.

[0009] Wherein, the step 2 specifically includes:

[0010] Calculate the equivalent steady-state effective value of the electric shock current of the mine power supply system;

[0011] Calculate the transient effective value of electric shock current in the mine power supply system;

[0012] Calculate the effective value of zero-sequence voltage of mine power supply system;

[0013] Calculate the zero-sequence voltage change rate of the mine power supply system;

[0014] Calculate the instantaneous value of zero-sequence voltage of mine power supply system;

[0015] Calculate the effective value of each phase-to-ground voltage of the mine power supply system;

[0016] Calculate the voltage change rate of each phase to ground of the mine power supply system;

[0017] Calculate the instantaneous value of each relative ground voltage of the mine power supply system;

[0018] Determine whether an asymmetric ground fault occurs by sampling the waveform shape of the current;

[0019] Parameter sampling method that does not affect the neutral point wiring mode of the mine power supply system;

[0020] Furthermore, the calculation of the equivalent steady-state effective value of the electric shock current of a person in the mine power supply system includes:

[0021] When a single-phase grounding fault or electric shock accident occurs in the power supply system, the equivalent circuit diagram is drawn according to the Thevenin equivalent theorem considering the ground distribution parameters; the effective value of the electric shock current is:

[0022]

[0023] Furthermore, the calculation of the transient effective value of the electric shock current of the mine power supply system includes:

[0024] Based on the equivalent voltage source model, the equivalent circuit diagram at this time is drawn, and the waveform of the human electric shock current at this time is calculated; under the same parameters, MATLAB / Simulink is used for simulation to obtain the simulation waveform of the human electric shock current, and the differential equations are solved to obtain the transient effective value of the human electric shock current.

[0025] Further, the calculating of the effective value of the zero-sequence voltage of the mine power supply system includes:

[0026] Connect the three sampling capacitors to the A, B, and C phases of the power grid respectively, and connect the other ends together through a micro current transformer to form an artificial neutral point, which is then grounded through the primary side of a micro current transformer. When the power supply system is in a steady state, the zero-sequence voltage phasor formula is: The effective value of the zero-sequence voltage is Phase lag in, is the primary current of the micro current transformer passing through the neutral point, C cy is the capacitance value of the sampling capacitor.

[0027] Further, the calculating of the zero-sequence voltage change rate of the mine power supply system includes:

[0028] The rate of change of zero-sequence voltage is obtained through the VCR of capacitor current and voltage.

[0029]

[0030] Further, the calculating of the instantaneous value of zero-sequence voltage of the mine power supply system includes:

[0031] The rate of change of zero-sequence voltage Integrating both sides, we can get the instantaneous value of zero-sequence voltage:

[0032]

[0033] Further, the calculating of the effective values ​​of the relative ground voltages of the mine power supply system includes:

[0034] The phase formulas of the three-phase voltages A, B, and C are The effective values ​​of the voltages A, B, and C relative to ground are

[0035]

[0036] Phase angle lag in, They are the primary side currents of the micro current transformer passing through the capacitors of phase A, phase B, and phase C respectively.

[0037] Further, the calculation of the relative ground voltage change rate of the mine power supply system includes:

[0038] Through the VCR of capacitor current and voltage, the change rates of the voltages A, B, and C relative to ground are obtained as follows:

[0039] Further, the calculation of the instantaneous values ​​of the relative ground voltages of the mine power supply system includes:

[0040] The rate of change of the voltage between A, B and C By integrating both sides, we can get the instantaneous value of the voltage between A, B, and C to ground:

[0041] Furthermore, whether an asymmetric grounding fault occurs is determined by sampling the current waveform shape, specifically:

[0042] Under different insulation drop conditions, the waveform shape is different when an asymmetric grounding fault occurs, and the insulation resistance drop condition can be judged by the waveform shape.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] 1) Compared with the traditional zero-sequence voltage measurement method, the present invention does not change the neutral point grounding method of the power system. Keeping the grounding method unchanged can maintain the balance and stability of the system and reduce faults and hidden dangers of the power system.

[0045] 2) The equipment manufactured according to this method is small in size, easy to install and maintain, and can reduce the failure rate of the equipment. Maintenance personnel can more conveniently inspect and maintain the equipment, reducing maintenance time and maintenance costs. Compared with the traditional zero-sequence voltage measurement method, this method reduces the manufacturing cost, transportation cost and installation cost of the equipment.

[0046] 3) In transient conditions, it can measure the instantaneous value of zero-sequence voltage in real time, providing a sampling device for the new transient leakage protection algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings generally illustrate various embodiments by way of example and not limitation, and together with the description and claims, serve to illustrate the embodiments of the invention. Where appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.

[0048] Figure 1 A diagram of a power supply system with a neutral point not grounded according to the present invention is shown;

[0049] Figure 2 The equivalent circuit diagram of electric shock to human body of the present invention is shown;

[0050] Figure 3 The waveform of the sampled current of the current micro-transformer after three capacitors when a fault occurs is shown. DETAILED DESCRIPTION

[0051] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0052] An embodiment of the present invention provides a leakage protection method for a mine power supply system, comprising:

[0053] Step 1: Connect three sampling capacitors to the A, B, and C phases of the power grid respectively, and connect the other ends together through a micro current transformer to form an artificial neutral point, which is then grounded through the primary side of a micro current transformer.

[0054] Step 2, monitoring the zero-sequence voltage, zero-sequence voltage change rate, each relative-to-ground voltage and each relative-to-ground voltage change rate of the three-phase three-wire power supply system, while considering the line distribution parameters, so as to quickly and accurately sample multiple parameters such as the zero-sequence voltage effective value, the zero-sequence voltage change rate, the zero-sequence voltage instantaneous value, the relative-to-ground voltage effective value, the relative-to-ground voltage change rate, the relative-to-ground voltage instantaneous value, the waveform shape of the sampling current, etc. when different types of leakage faults occur;

[0055] Calculate the equivalent steady-state effective value of the electric shock current of the mine power supply system;

[0056] Calculate the transient effective value of electric shock current in the mine power supply system;

[0057] Calculate the effective value of zero-sequence voltage of mine power supply system;

[0058] Calculate the zero-sequence voltage change rate of the mine power supply system;

[0059] Calculate the instantaneous value of zero-sequence voltage of mine power supply system;

[0060] Calculate the effective value of each phase-to-ground voltage of the mine power supply system;

[0061] Calculate the voltage change rate of each phase to ground of the mine power supply system;

[0062] Calculate the instantaneous value of each relative ground voltage of the mine power supply system;

[0063] Determine whether an asymmetric ground fault occurs by sampling the waveform shape of the current;

[0064] Parameter sampling method that does not affect the neutral point wiring mode of the mine power supply system;

[0065] Step 3: Zero-sequence current flows through the fault resistor, the earth, and the insulation resistance r of the grid to the earth. A , r B , r C Return to the power supply. If the equivalent resistance decreases and the detection current increases, the current transformer collects the current increase, calculates that various parameters reach the set value, and the protection device is activated to complete the leakage protection.

[0066] Embodiment 1:

[0067] Analyze the situation of electric shock in the system. Low-voltage power supply system is mostly neutral point ungrounded. Its circuit structure is as follows Figure 1 shown.

[0068] Figure 1 Medium R r is the human body resistance, r A 、r B 、r C is the insulation resistance of the power supply system to ground, C A , C B , C C is the system's distributed capacitance to ground. According to Thevenin's equivalence theorem, draw Figure 1 The equivalent circuit diagram is as follows Figure 2 shown.

[0069] For the convenience of analysis, it is assumed that the distributed capacitance of each phase to ground is equal, and the insulation resistance of each phase to ground is also equal, then

[0070] C Σ =C A / / C B / / C C / / C cy / / C cy / / C cy =3(C+C cy ) (1)

[0071]

[0072] Substituting equation (3) into equation (4), we can obtain

[0073]

[0074] It is the primary current of the micro current transformer passing through the A-phase capacitor.

[0075] The equivalent steady-state effective value of the electric shock current of the mine power supply system can be obtained from formula (5) and (6):

[0076]

[0077] Among them, I Acy It is the effective value of the primary current of the micro current transformer passing through the A-phase capacitor.

[0078]

[0079] The transient effective value of the electric shock current in the mine power supply system can be obtained from equations (5) and (8):

[0080]

[0081] The zero-sequence voltage phasor formula is

[0082]

[0083] The effective value of the zero-sequence voltage is

[0084]

[0085] It is the primary current of the micro current transformer passing through the neutral point.

[0086] Through the VCR of capacitor current and voltage, the rate of change of zero-sequence voltage is obtained.

[0087]

[0088] Similarly, we can get the voltage change rate of A relative to ground

[0089]

[0090] Integrating both sides of equation (12) yields the instantaneous value of the zero-sequence voltage.

[0091]

[0092] Under different insulation drop conditions, it is observed that the waveforms of the sampled currents of the current micro-transformers behind the three capacitors are different. The waveforms of the sampled currents corresponding to the insulation drop of single-phase, two-phase and three-phase are shown in the figure below. Figure 3 .pass Figure 3 From the waveform diagram, we can see that the waveform shapes are different when single-phase insulation drop, two-phase insulation drop and three-phase insulation drop occur. The insulation resistance drop can be judged by the waveform shape.

[0093] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A leakage protection method for multi-parameter sampling of a mine power supply system, characterized in that: The following steps are involved: The three sampling capacitors are connected to the A, B, and C phases of the power supply system respectively, and the other ends are connected through a micro current transformer to form an artificial neutral point, which is grounded through the primary side of another micro current transformer. The above-mentioned power supply system is monitored and the equivalent steady-state effective value of the electric shock current of the power supply system, the transient effective value of the electric shock current of the power supply system, the effective value of the zero-sequence voltage of the power supply system, the rate of change of the zero-sequence voltage of the power supply system, the instantaneous value of the zero-sequence voltage of the power supply system, the effective value of each relative ground voltage of the power supply system, the rate of change of each relative ground voltage of the power supply system and the instantaneous value of each relative ground voltage of the power supply system are calculated, and the waveform shape of the sampled current is collected; The fault is determined based on the above calculated data, the protection device is activated, and leakage protection is completed.

2. The leakage protection method for multi-parameter sampling of a mine power supply system according to claim 1, characterized in that: The formula for calculating the equivalent steady-state effective value of the electric shock current of the power supply system is: When a single-phase grounding fault or electric shock accident occurs in the power supply system, the ground distribution parameters are considered, and the equivalent circuit diagram is drawn according to the Thevenin equivalent theorem. The effective value of the electric shock current is obtained according to the effective value calculation formula of the electric shock current. The formula is: in, is the voltage between A and ground, Z is the distribution parameter between A and ground, R r For human resistance, Electric current for personal electric shock.

3. The leakage protection method for multi-parameter sampling of a mine power supply system according to claim 1, characterized in that: The calculation of the transient effective value of the electric shock current of the power supply system is specifically as follows: Based on the equivalent voltage source model, the equivalent circuit diagram at this time is drawn, and the waveform of the human electric shock current at this time is calculated; under the same parameters, MATLAB / Simulink is used for simulation to obtain the simulation waveform of the human electric shock current, and the differential equations are solved to obtain the transient effective value of the human electric shock current.

4. The leakage protection method of multi-parameter sampling of mine power supply system according to claim 1 is characterized in that: The specific formula for calculating the effective value of the zero-sequence voltage of the power supply system is: Among them, I cy is the effective value of the primary current of the micro current transformer passing through the neutral point, ω is the angular frequency, when the power frequency is 50Hz, ω=100π, C cy is the capacitance value of the sampling capacitor.

5. The leakage protection method of multi-parameter sampling of mine power supply system according to claim 1 is characterized in that: The calculation of the zero-sequence voltage change rate of the power supply system is specifically: When a single-phase leakage fault occurs in the power supply system, the power supply system enters a transition process. The change rate of the zero-sequence voltage is calculated through the VCR ratio of the capacitor current to the voltage, which is: Among them, i cy is the instantaneous current on the primary side of the micro current transformer passing through the neutral point, C cy is the capacitance value of the sampling capacitor.

6. The leakage protection method of multi-parameter sampling of mine power supply system according to claim 1, characterized in that: The calculation of the instantaneous value of the zero-sequence voltage of the power supply system is specifically: Integrating both sides of the rate of change of the zero-sequence voltage gives the instantaneous value of the zero-sequence voltage, specifically: Among them, i cy is the instantaneous current on the primary side of the micro current transformer passing through the neutral point, C cy is the capacitance value of the sampling capacitor.

7. The leakage protection method of multi-parameter sampling of mine power supply system according to claim 1, characterized in that: The specific calculation of the effective value of each relative voltage is: By calculating the voltage phasors of the three-phase electricity A, B, and C to the ground, the effective value of the voltage between each phase and the ground is obtained, which is: Among them, I Acy is the effective value of the primary current of the micro current transformer passing through the A-phase capacitor, I Bcy is the effective value of the primary current of the micro current transformer passing through the B phase capacitor, I Ccy is the effective value of the primary current of the micro current transformer passing through the C phase capacitor, ω is the angular frequency, when the power frequency is 50Hz, ω=100π, C cy is the capacitance value of the sampling capacitor.

8. The leakage protection method for multi-parameter sampling of a mine power supply system according to claim 1, characterized in that: The specific calculation of the voltage change rate of each phase is: Through the VCR of capacitor current and voltage, the change rates of the voltages A, B, and C relative to ground are obtained as follows: Among them, i Acy is the instantaneous current on the primary side of the micro current transformer passing through the capacitor of phase A, i Bcy is the instantaneous current on the primary side of the micro current transformer passing through the B phase capacitor, i Ccy is the instantaneous current on the primary side of the micro current transformer passing through the C phase capacitor, C cy is the capacitance value of the sampling capacitor.

9. The leakage protection method of multi-parameter sampling of mine power supply system according to claim 1, characterized in that: The calculation of the instantaneous value of each relative voltage to ground is specifically as follows: The instantaneous values ​​of the three-phase voltages A, B, and C are obtained by integrating the rates of change of the three-phase voltages A, B, and C. The formula is: Among them, i Acy is the instantaneous current on the primary side of the micro current transformer passing through the capacitor of phase A, i Bcy is the instantaneous current on the primary side of the micro current transformer passing through the B phase capacitor, i Ccy is the instantaneous current on the primary side of the micro current transformer passing through the C phase capacitor, C cy is the capacitance value of the sampling capacitor.

10. The leakage protection method of multi-parameter sampling of mine power supply system according to claim 1, characterized in that: Whether an asymmetric grounding fault occurs is determined by sampling the current waveform shape, specifically: Under different insulation drop conditions, the waveform shape is different when an asymmetric grounding fault occurs, and the insulation resistance drop condition can be judged by the waveform shape.

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